Civic Issues Blog: Fracking

I thought I would start off my second discussion on Marcellus shale on what it is exactly and how the natural gas it contains is extracted. The Marcellus Formation is a wide belt of shale that can be found underneath southern New York, eastern Ohio, West Virginia, and over half of Pennsylvania. It formed in the Devonian Period (approximately 420-360 million years ago) and has massive natural gas deposits in the pores of the rock due to prehistoric organisms decomposing in the subterranean sediment and being heated from geothermal energy. Obviously, with America’s dependence on foreign oil being a concern, this is a great resource to have to solve that problem. Knowledge of the formations natural gas capabilities have been known since the 1973 energy crisis, but the rock’s potential was not pursued because improper drilling techniques could not efficiently extract the gas. In the 1990’s a new system for extracting natural gas from shale formations was developed in Texas for the Barnett Shale formation. The new “slick-water frac” system was finally able to efficiently extract gas from deep pockets. It would later be known as hydraulic fracturing, and informally, fracking.

marcellus-shale-depth-map

The hydraulic fracturing process begins by drilling vertically as deep down as 10,000 feet, but most often 5,000 to 9,000 feet. A steel casing is put down this well, and sealed from the surrounding rock with concrete. From there, the process varies. Most companies have begun to drill horizontally after first drilling vertically. This is achieved with a MWD drill bit, which creates a curve, entering the shale at a totally vertical position, allowing more shale to be processed with one drilling rig. From there a second casing is added and sealed just like the first. Next, a “perf” gun is placed down the casing at the extraction point. Small explosions from the gun create perforations in the casing and break the surrounding shale. Then, hydraulic fracturing fluid (also known as frac water) is pumped down the well at extreme pressures, causing more shale to be crushed through the perforations created by the explosion. We’ll talk more about the “water” later. Finally, the natural gas is released from the pores of the rock and captured at the surface. The whole formation is expected to contain as much as 363 trillion cubic feet of natural gas, and some wells are reporting to extract as much as 3 million cubic feet a day. To put that in perspective, 363 trillion cubic feet of natural gas is enough energy to power the US for 14 years.

marcellus-gas-well

Sounds pretty good doesn’t it? But there’s a problem. Remember the frac water? About 750 different chemicals have been identified to have been used by gas companies in their hydraulic fracturing fluid. These chemical additives help the fluid dissolve more rock, flow down the well, and in the case of sand and plastic pellets, create additional pressure and abrasion of the shale. Some chemicals based from chloride, barium, ammonium, sodium, and even arsenic can be very harmful to humans and the environment. Though these gas wells are drilled far below those used for drinking water, no nearer than 200 feet in the case of structures, water wells, or springs, and 100 feet from streams and wetlands, cracks in the surrounding rock and faulty casings can lead to pollution. After the frac water has been used, it is sometimes recycled and used again in other wells. Eventually though, most of it ends up on big trucks that dot the roads of Pennsylvania, transporting it to sewage treatment plants that treat the water and release it into our rivers. Of course leaking trucks, traffic accidents, and bad treatment can lead to disaster in this step of the process too. Trust me, I live in Western PA, I’ve driven behind frac trucks and seen them in enough parking lots to tell you they get rusty and leak. Even methane from the disturbed rock formations can rise up through the limestone and pollute wells that are only drilled as deep as 200 feet. Which leads into what I will be discussing next time, the pollution due to Marcellus shale drilling and my first hand experiences with it.

Citations:    dcnr.state.pa.us     exploreshale.org

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